["Clinical Psychology &Psychotherapy, Volume 33, Issue 2, March/April 2026. ", "\nABSTRACT\nMental disorders affect not only mothers themselves but also their children and partners. Borderline personality disorder (BPD) in particular is thought to impact the mother–child relationship, but comparisons with mothers with other mental disorders are scarce. Many studies use questionnaires without examining if self‐report corresponds to observable behaviour. We assessed the perceived mother–child relationship using the Parenting Relationship Questionnaire and the Child Relationship Behaviour Inventory in three groups: (1) mothers with BPD, (2) mothers with anxiety and/or depression and (3) mothers without mental disorders with preschool children. Additionally, mother–child interactions during free‐play and structured tasks were video‐recorded and coded using the Coding Interactive Behaviour system. Compared with mothers without mental disorders, both clinical groups perceived their relationship with the child, their own parenting skills and their children's behaviour as less positive. Mothers with BPD felt less confident and more frustrated than those with anxiety and/or depression. No significant group differences emerged in observed behaviour (e.g., sensitivity, intrusiveness), and correlations between self‐report and observation were low. Overall, mothers with BPD face similar challenges as mothers with anxiety or depressive disorders, but they experience particular distress when it comes to relating to and controlling their child's affect. While mothers in both clinical groups are able to foster positive relationships with their children in a controlled laboratory setting, they find it difficult to maintain these skills permanently (e.g., during negative child affect).\nTrial Registration: DRKS‐ID: DRKS00020460\n"]